Electromagnetic transformer unit



Aug. 9, 1966 c. F. SCHROEDER ELECTROMAGNETIC TRANSFORMER UNIT 5Sheets-Sheet 1 Filed NOV. 30, 1962 INVENTOR. I

g- 1966 c. F. SCHROEDER ELECTROMAGNETIC TRANSFORMER UNIT 5 Sheets-Sheet2 Filed NOV. 30., 1962 IN'VENT0R. 67/42: 5 E SCHIPOEDEI? 'Aug- 1966 c.F. SCHROEDER 3,265,851

I ELECTROMAGNETIC TRANSFORMER UNIT Filed Nov. 30, 1962 3 Sheets-Sheet 5INVENTOR. 0mm 5 E Samoa-on? appliance of industrial purposes.

United States Patent ELECTROMAGNETIC TRANSFORMER UNIT Charles F.Schroeder, 2317 ValleybrookDrive,

- Toledo 15, Ohio Filed Nov. 30, 1962, Ser. No. 241,208 3 Claims. (Cl.219-10.77)

The present invention relates to an electromagnetic transformer unit,and more particularly, a heater unit utilizing a closed secondarywinding in such manner as to make the unit adaptable to performance in awide range of specific devices for different heating purposes.

According to the present invention, a magnetic circuit construction .isprovided which, although capable of design for operation at any of awide range of frequencies, is highly adaptable to the translation ofelectrical energy into heat energy at the usual commercial frequenciesof 50 or 60 cycles and even lower frequencies, such as 25 cycles stilloccasionally encountered in practice.

It is a purpose of the invention to provide a magnetic circuitconstruction incorporating principles which make it adaptable toprovision of heating units for translation of electrical energy intoheat energy at commercially available power frequencies with a minimumofcost in equipment.

It is another object of the invention to provide a new electricalheating unit flexibly adaptable to any of a wide variety of uses byproportionalchanges in shape within the latitude of variation permittedby the-principles 1 employed.

In brief, the operating-elementsof the construction of the inventionincludes a magnetic core energized .by a primary winding, and a singleturnsecondary loop which surrounds both the core andprimary to provide aheating unit arrangement flexibly utilizable for either home This isaccomplished in general by surrounding-a magnetic circuitloop with asecondary, notonly closed about the cross section-of the core, but alsoextending along the length of the magnetic circuitand forming a closedloop.

A feature of the invention lies in its adaptability in design topractically any commercial voltage and fre- -quency without need forspecial auxiliary-frequency-generat-ing equipment.

Another feature of the invention lies in its ruggedness of constructionand adaptability to provision of selective surface areas to be heated tohigh temperatures, while other portions of the unit remain substantiallycool.

Still another feature of the construction of this invention lies in itsefficiency in translation ofelectrical energy .taken in connection withthe accompanying drawings, -in which:

Although for purposes of illustration, this invention is .hereindescribed in connection With the translation of electrical energy intoheat, it will be understood upon review of the embodiments disclosed,that they are adapt able for other purposes as well, such for example,as

where large magnet flux concentrations are desirable and are produced asa result of high currents in the closed secondary loop.

FIGURE 1 is an isometric view, partially broken away .and partially incross-section, illustrating a magnetic circuit construction embodyingthe principles of my invention;

loop drawn in the shell wall in FIGURE .1.

"ice FIGURE 2 is an isometric view, partially broken away and partiallyvin cross-section, of an electrically heated kettle embodying themagnetic circuit principles of my invention;

.FIGURE 3 is a partially broken away and partially cross-sectional viewof an extrusion press cylinder embodying a plurality of magnetic circuitsections according to the principles of my invention; 7

FIGURE 4 is an isometric partially broken cross-sectional view of ahot-plate type unit embodying the prin- .partially broken away andpartially in cross-section of a heater strip embodying the principles ofthe presentinvention;

FIGURE 7 is an enlarged broken cross-sectional view of a. portion of theheater strip of FIGURE 6; and

FIGURE 8 is a semi-schematic illustration of a heating unit embodyingthe principles of the present invention adapted to integral associationof a temperature control circuit.

Referring to the drawings in greater detail, FIGURE 1 shows the generalarrangement of components of a transformer type constructionlt)employing a single turn secondary loop wherein the single turn loopcomprises the outer shell made up of an annular member of U- shapedcross-section capped by a flat ring-shaped capping member which forms anenclosure and completes a.closed able of permitting a low resistancejuncture of the ring .cap 12 and the member 11 to establish alowresistance loop about the magnetic core enclosed therein. The mag-.neticcore-13 is made up of magnetic flux path segments and in thisrespect, can for example, be'a spiral wound core or a series of stackedannular discs or even a magnetic Wire wound core. The primary orenergizing winding 14 is wound directly on the. coreoverelectricalinsulation of high temperature-resistant properties. Thepri- .mary winding as illustrated may extend over the full length of thecore, and correspondingly extend through the interior of the annularsecondary for its entire length. The leads 15 for the primary winding 14are connected .to plug-type connector prongs '17 mounted oncaninsulating member 16 installed in the side of the annular secondary.

FIGURE '1 illustrates that the annular members 11 .and '12, in a sense,form a pair of secondary loops. One

closed loop is formed by thecross-sectional pathof the shell for thecore 16, while the other loop is provided .longitudinally by the annularshape of the shell.

In operation, energization of the primary winding 14- generates amagnetic flux in the core 13. This flux cuts the walls of thesurrounding shell and generates a secondary current having apathextending around the crosssection of the shell. This is illustratedby the dashed-line Since the magnetic flux alternates, the current flowin the cross-sectional loop is also alternating. Accordingly, doubleheaded arrows are utilized to illustrate the path of flow of suchcurrent. Any tendency toward flux leakage diametrically acrossthecannularcore results in generation of an annular current flow,- inaddition to .the flow in the cross-sectional loop. 'Suflicient currentcan be readily made to flow, particularly in the cross-sectional loop,to result in the temperature of the unit being raised to a degreepermitting its utilization as a heater unit.

FIGURE 2 shows a heating kettle embodying the principles of thetransformer unit of FIGURE 1 for translation of electrical energy intoheat for cooking purposes. In this embodiment, the closed loop secondaryis formed of the hollow shell-like walls of the kettle made up of athick outer wall 21 and a thin inner wall 22. Since the current flow inthe secondary is predominantly in the cross-sectional loop, the currentflow in the thick outer wall equals that of the thin interior wall ofthe kettle. Thus, when the annular-shaped core 23 encased within thecrosssectional loop is energized by the primary coil 24 wound thereon,the current flow in the cross-sectional loop will cause by far thegreatest 1 R loss in the interior wall 22 effecting translation of theenergy into heat. In the opposite sense, however, the outer thicker wall21 of the cross-sectional loop can be made sufliciently thick that itwill remain relatively cool while the interior wall 22 is raised todesired temperature.

Although the core 23 is shown extending through substantially' the fullheight of the heating kettle, it can also be made shorter under certainelectrical design criteria and not so long as to extend through the fulllength of the hollow walled structure. That is, the hollow interior ofthe unit can be made to extend a distance beyond the core and also bemade narrower, if desired, to conform to desired exterior designconfigurations.

Upon reviewing'the path of current flow in the secondary briefly, againit will be noted that when the magnetic flux build-up and collapseoccurs within the core 23, the current flow in the closed secondary loopformed by joinder of the thin interior wall 22 to the thicker exteriorthrough the overhanging edge of the thick wallsection 21 and itsbridging bottomportion 26, can be made such that the temperature of theinterior will be raised appreciably while the thicker sections 21 and 26will not experience an appreciable rise in temperature. Thus, theexterior of the heating kettle can be maintained cool, while theinterior is of sufiicient temperature to heat its contents, such as foodplaced therein to be cooked.

To further enhance the efiiciency of utilization of the kettle, theexterior can be made of relatively low electrical resistance materialssuch as aluminum, while the interior is made of steel having higherresistivity as well as a magnetic hysteresis which will provide acorresponding larger capability for generation of heat with a givenmagnitude of current flow in the secondary loop. Electrical and thermalinsulation 28, such as asbestos or fibrous glass,

is inserted between the core 23 and the interior wall 22 to bothelectrically isolate the walls and to thermally insulate the core fromthe hot interior Wall. Thus, the core, by having an interior diameterdimension somewhat larger than the diameter of the thin interior wall,is both isolated by space as well as the thermal insulation interposedtherein. The interior wall and the exterior walls are joined such as bywelding them together at their zone of juncture at the top of the kettleas at the bridging projection 26. If desired, the exterior can be coatedwith a protective layer of material such as an epoxy resin. Handles 29are provided at the exterior and an electrical plug 25 connected to thewinding 24 is provided for convenient connection to a power source suchas a 60 cycle power source.

FIGURE 3 illustrates another unit incorporating the transformerconstruction of my invention for heating purposes. This apparatusutilizes a series of circular transformer sections physically aligned toform a hollow cylinder such as the interioir of a resin extrusion press.The common interior wall 32 of the cylinder is raised to a desiredtemperature while the thicker exterior which makes a series of adjacentclosed loop secondaries with the interior wall 32 is maintainedrelatively cool. Within each closed loop secondary is a magnetic core ofannular shape 33 extending about the cylindrical interior. Each core 33is enclosed by the outer shell 31 which provides a pair of radiallyinwardly extending annular projections 35 located on opposite sides ofthe core between the shell and the interior wall 32. The interior wall32 is sufiiciently thin in dimension that it can be readily heated bycurrent flow therethrough while the exterior shell 31 of largerthickness will not become appreciably heated by the same current. Eachcore 33 has an insulated primary winding 34 wound thereon while thermalinsulating material is interposed between the core and the interior wall32 of the cylinder. Thus, the core is thermally and electricallyinsulated from the interior wall.

The series of spaced cores 33 so arranged about and along the length ofthe interior wall 32, are well adapted to independent energization ofadjacent zones to estab lish different desired temperatures along thelength of the cylinder. At the front of the cylinder, a nozzle 36 isprovided, as shown in dotted lines, having an aperture 39 through whichmaterial from the interior of the cylinder is extruded into a mold 37also outlined in dotted lines. A feature of this arrangement lies inthat the material extruded under pressure from such cylinder can beintimately regulated so that the material can be heated or allowed tocool to different temperatures at each stage of its path of progressionalong the length of the cylinder.

FIGURE 4 illustrates still another embodiment of the present inventionwherein the transformer principles are utilized for generation of heatin a hot-plate type unit. In this construction, the hot-plate unit 40 isformed of a circular electrically conducting base 41 having an annularrecess therein for receipt of a magnetic core 43, also of annular shape.The core 43 has a primary winding 44 wound thereon over its full lengthand energized through the exterior wall of the recess by way of leads 45connected to suitable exterior power source. The circular base is cappedby a thin plate 42 enclosing the core 43. The recess in the base issufiiciently deep that thermal insulation 48 can be interposed betweenthe plate and the core with its energizing winding thereon. The base canbe made of material having a low resistivity such as aluminum, while thethin cap plate is made of a higher resistivity material such as steel sothat current flow in the loop formed by the base member and the coveringplate is most effective in translating the electrical energy into heatwithin the plate 42. The steel plate will generate heat due to bothhysteresis and eddy current losses in addition to resistance losses dueto the secondary current flow therein. The juncture between the basemember and the cover plate 42 can be effected in zones of smallercross-section formed by bevelling the base portions contacting the plateso that heat transmission to the base from the cover plate is minimized.

FIGURE 5 illustrates a fry pan unit utilizing the principles of thetransformer construction of FIGURE 4 in which the exterior of thetransformer remains cool while only the interior zones are raised to arelatively high temperature. In this connection, the core 53 is of flatannular shape with an insulated primary winding 54 wound directlythereon extending over the full length of the annual and enclosed by thebase 51 of thick cross-section forming a loop with an inserted flatplate member 52 having an upwardly extending wall 50. The outer shellformed of the base 51 has an upwardly projecting overhanging lip section59, while the plate member 52 inserted therein engages the interior ofthe lip 59 by way of its Wall 50 to form an electrical loop therewith.The shell 51 also has a central projection 58 centrally engaging theunder portion of the plate member 52, thereby forming a closed annularsecondary loop about each increment of length of the core 53. Thewinding 54 on the core 53 has a pair of leads 55 extending through thewall of the shell 51 to a suitable connecting plug (not shown) on thehandle 56 of the fry pan. Thermal insulation 57 is interposed betweenthe core 53 and the bottom of the hot plate 52 to thermally insulate thecore from the heating portion of the fry pan.

FIGURES 6 and 7 illustrate a kitchen-range type elec- 'trical heatingelement embodying the principles of this invention. The heating elementhere is shaped generally to look like those used in kitchen electricalranges but utilizes magnetic principles in conjunction with the usualresistance heating principles to translate electrical energy into heat.An annular tube 61 of electrically conducting material encloses a core63 of magnetic material electrically energized by a primary winding 64connected to a pair of connecting prongs 65 adapted for association witha plug '66 connected to a source of electrical energy. The magnetic coreis embedded within a high temperature resistant electrical insulatingmaterial such as a ceramic material 68 and can be laminated or in theform of a generally circular cable of wire conductors extending aboutthe interior of the annular tube to form a complete annular magneticcore. The winding 64 generates magnetic flux in the core which cuts thecircular wall of the tube to cause a current flow therein andconsequently effect heating of the tube. For more efiicient localtransfer of heat to utensils place-d thereon, the tube 61 is providedwith a thinwalled upper portion or top 62 of material having a highelectrical resistivity, thereby concentrating the heat in the upper zoneof the annular loop (ill and correspondingly making it more quicklyresponsive in temperature to energy changes.

The primary winding 64 can be made of resistance Wire such as Nichromewire, which of itself will generate heat when energized in a mannersimilar to the electrical resistance heaters conventionally utilized. Inaddi tion to resistance heating, however, the tube in this arrangementtranslates magnetic energy into heat directly in the walls of the tube61 before heat is conducted thereto from the resistance wire through theinsulating materials; Thus, a combination of resistance and magneticheating of the tube 61 is provided which is much quicker in startup thanstraight resistance-type heating elements, since heat is generated inthe outer walls as soon as electrical energy is supplied.

To reduce transfer of heat to the magnetic core 66 from the primarywinding, the core is provided with an electrical and thermal insulationcovering 67 such as asbestos paper over which the energizing resistancewinding 64 is wound. Both the magnetic core and the resistance Wire areelectrically isolated from the outer shell by the ceramic insulatingmaterial 68 within which they are embedded. Although resistance heatingis here described, the primary can also be made to generate heatprincipally by current flow in the surrounding walls as in thearrangement of the foregoing embodiments. Where the resistance wire isutilized for the primary, however, the core may be more desirablydisposed closer to the top of the space within the tube 61 so that theheat will be more readily conducted, through the heating surface fromthe resistance wire rather than to the side walls or the bottom.

FIGURE 8 illustrates a heating unit and the adaptability of the presentinvention to regulation by temperature control means Without need forlarge power control elements. In this arrangement, the heating unit isan assembly of a close-d loop secondary 102 of annular shape enclosing amagnetic core 103, beside being provided with a primary winding 104within the secondary loop 102, has a second or control winding 105 whichprovides a saturating magnetic flux. The primary winding 104 isenergized in conventional manner by the line leads L1, L2 connected to asuitable source of alternating current, while the second winding 105 isconnected to the line leads L1 and L2 through a rectifier 1'15 andbridge circuit. The second Winding 105 is energized by D.C. under thecontrol of a bridge circuit having an associated temperature sensingmeans such as a thermistor connected therein. The magnetic fluxgenerated by the primary winding 104 thus can be regulated ineffectiveness to translate the electrical energy into heat by a settingof manually adjustable control components associated with the bridge.

The bridge circuit of FIGURE 8 is essentially a Wheatstone bridge typecircuit having a thermistor or other temperature sensing element such asa thermocouple 117 connected therein, while the remaining bridgeresistances 118, 119, and 120 are connected so that setting of thevariable resistance 118 will determine the amount of energy convertedinto electrical power in the closed secondary 102, and correspondinglyfix the degree of temperat-ure rise and temperature of the tube 102. Thethermocouple is positioned on a section of the secondary which isrepresentative of the temperature of the heating unit, and by settingthe variable resistance 1 18 to a temperature setting determined bycalibration, the balance of current flow in the bridge determines thesaturating D.C. current flowing in the winding 105. The resistance 118can be accurately calibrated for temperature to be maintained at theheating unit so that when a temperature setting is made, a D.C. magneticflux will be generated in the core such as will permit generation of theproper amount of flux due to current flow in the Winding 104corresponding to the desired temperature.

Saturation of the core 103 by the second winding can be carried to avalue such that little or substantially no heating of the secondary tube102 will occur. On the other hand, the setting can be adjusted so thatthe degree of saturation by the D.C. winding 10 5 is nil to permit fulltranslation of the electrical energy of the winding 104 into heat energyin the tube 102. Thus, with a single setting of the relatively lowcurrent capacity resistance in the bridge circuit, the larger current ofthe secondary tube and translation of electrical energy into heat withinthe system can be fixed.

'I'his bridge arrangement, however, is only exemplary of one of manybridge control arrangements which can be adapted to the units of thepresent invention. For example, impedance type bridges, as well as anynumber of other types of electrical bridge networks can be utilized witha temperature sensing mechanism to provide saturation controls forsetting temperature of the heating unit.

In view of the foregoing, it will be understood that many variations ofthe present invention can be provided within the broad scope of theprinciples embodied therein. For example, the transformer, although asillustrated, is predominantly adopted to use for heating units, it willbe recognized that the transformer construction as illustrated in FIGURE1 can be utilized for other magnetic circuit arrangements, such asprovision of an energizing circuit for still another loop extendedthrough the opening in the annular configuration illustrated. Themagnetic flux concentration in the sec-ondary, and about the secondaryof the construction is also of novel character, and any number ofadaptations of the trans-former principles here disclosed can beaccomplished. Thus, while particular embodiments of the invention havebeen shown and described, it is intended by the appended claims to coverall such modifications which fall within the true spirit and scope ofthe invention.

I claim:

1. Heating apparatus of the character disclosed, comprising incombination, a magnetic core in the form of a magnetic loop closed onitself, a primary electrical winding wound on said core, a secondaryelectrical circuit closed on itself about the cross-section of said coreand extending along the length of said magnetic core loop, a magneticsaturating means associated with said core for establishment of aselectable degree of magnetic saturation of said core thereby toadjustably fix the magnitude of current flow and heat generated by saidsecondary loop, and a temperature sensing means communicating intemperature sensing relation with said secondary loop, said temperaturesensing means being operably associated with said saturation means tomaintain the temperature of said secondary at a predetermined desiredvalue.

2. Heating apparatus according to claim 1 wherein 7 8 the magneticsaturating means is variable and produces 1,507,005 9/1924 Shaw et a1.219- -10 .5 1 a magnetic flux in said core supplementing the flux in-1,750,958 3/1930 Goshorn 2l9l0.51 duced therein by said primary Winding.2,338,236 1/1944 Ferris 219465 3. Heating apparatus according to claim 1wherein 2,783,343 2/1957 Co11opy- 21910.47 the secondary circuit extendsalong the full length of 5. 2,785,265 3/1957 Salisbury 2l9--l0.79 saidmagnetic core. 2,799,822 7/ 1957 Dewitz 32389.2

References Cited by the Examiner FOREIGN F UNITED STATES PATENTS 504,8805/1939 Great Britain. 7, 7/ 1 9 SnO-W 21910.79 X 10 RICHARD M. WOOD,Primary Examiner. 891,657 6/1808 Berry 21910.49 1,052,119 2/1913Anderson 219 10.79 ANTHONY BARTIS Examme" 1,289,210 12/1918 Lincoln21910.49 L. H. BENDER, Assistant Examiner.

